Process for making tobacco smoke filters

ABSTRACT

THE QUANTITY OF PLASTICIZER ADDED TO CELLULOSE ACETATE FILTER FIBERS IS CONTROLLED BY ADDING AN INDICATOR SUBSTANCE TO THE PLASTICIZER, THE INDICATOR SUBSTANCE HAVING DIFFERENT INFRARED ABSORPTION CHARACTERISTICS TO THOSE OF THE CELLULOSE ACETATE, AND MEASURING THE INFRARED REFLEXION OF THE PLASTICIZER-INDICATOR MIXTURE.

July 18, 1972 RABAN ET AL 3,677,806

PROCESS FOR MAKING TOBACCO SMOKE FILTERS Filed May 6, 1970 2 Sheets-Sheet 1 FIG] July 18, 1972 J RABAN ET AL PROCESS FOR MAKING TOBACCO SMOKE FILTERS 2 Sheets-Sheet 2 Filed May 6, 1970 US. Cl. 117-104 R 11 Claims ABSTRACT OF THE DISCLOSURE The quantity of plasticizer added to cellulose acetate filter fibers is controlled by adding an indicator substance to the plasticizer, the indicator substance having differ ent infrared absorption characteristics to those of the cellulose acetate, and measuring the infrared refiexion of the plasticizer-indicator mixture.

This application is a continuation-in-part of Ser. No. 798,637, filed Feb. 12, 1969, now abandoned.

The present invention relates to the production of tobacco smoke filters and more particularly to methods for setting or controlling the quantity of plasticizer applied to the spread out fiber material in tow form for cigarette and other tobacco smoke filters. The invention is more specifically concerned with filters consisting of cellulose acetate fiber bundles containing or treated with a binding agent on an ester basis acting as a plasticizer.

Known binding agents on an ester basis having a plasticizing efiect include glyceryl esters. It has been found that glycerine triacetate is particularly suitable for production of filters of crimped cellulose acetate fibers owing to its comparatively high boiling point and its capability of binding the individual fibers together at room temperature.

Although the use of esters as plasticizers has come to be generally accepted for the production of tobacco smoke filters of cellulose acetate fibers, certain disadvantages are found to occur.

Thus, for example, the determination of the amount of plasticizer added to the spread out filter material can only be performed by a complicated procedure. This procedure is carried out gravimetrically after the filter rod sections have already been produced, that is to say not during the actual application of the plasticizer. In accordance with departures from an empirically determined value for the amount of plasticizer which has been found acceptable in practice, the filter producing machine is adjusted so that the subsequently produced filters should contain the correct quantity of plasticizer. This production procedure not only involves a comparatively heavy personnel requirement but also brings with it a considerable amount of reject material because the filter producing machine can only be corrected after the filter material has been produced and until it is corrected, goes on producing defective filter rod sections.

A further disadvantage of the known method is the danger that generally used esters, such as glycerine triacetate, diffuse too rapidly into the cellulose acetate fibers. As a result the binding action is impaired, and if the plasticizer ceases to be present at the surfaces of the fibers of the filter owing to its being absorbed into the fibers the filtering action is decreased. As a result larger quantities of plasticizer must be added in order to compensate for the absorption. The presence of plasti- United States Patent Ofice;

3,677,806 Patented July 18, 1972 cizers such as glycerine triacetate which have a chemosorptive action, on the surface of the filter fibers is particularly necessary.

Furthermore, methods using known plasticizers have the disadvantage as regards the long time taken for hardening or curing, that is to say the time taken by the filter to become hard enough to be used by a smoker as part of a cigarette, and for the cigarettes to leave the factory.

Thus, for example, cellulose acetate filters treated with approximately 8% by weight glycerine triacetate require about 24 hours at room temperature to reach their prescribed degree of hardness. The filter rod sections must therefore be stored for this time. This brings with it the disadvantage that special precautions have to be taken in stacking the filter rod sections in order to avoid the underlying filter sections from becoming defomed by the pressure of the upper ones. Stacking is carried out in layers but even so may lead to reject material. The necessity for carrying out a curing treatment lasting 24 hours tends to make the rate of production very inflexible.

One object of the present invention is that of controlling the quantity of plasticizer applied to spread out filter material so that, on the one hand, the plasticizer is fully effective in the filter material and, on the other, reject filters are avoided.

One method for determining the quantity of a substance present in a production process without the necessity of taking samples of the substance is the continuous measurement of refiexion of infrared radiation.

Such a method of measurement has been previously proposed for moisture determination, see the book Feuchtemessung durch Infrarotreflexion published in Forschung in Hoechst Verlag Chemie Weilheim, Bergstrasse (1963), pages 119 et seq.

This method in the known form is, however, not practicable for cellulose acetate fiber material because the absorption bands of glycerine triacetate and cellulose acetate coincide.

The present invention consists in a method for controlling the application of plasticizer to tobacco smoke filter material, the plasticizer including an ester while the filter material includes fibers of cellulose acetate, comprising mixing a substance which has different infrared absorption characteristics to the cellulose acetate, with the plasticizer, as an indicator, measuring the infrared refiexion characteristics of the resulting mixture, spraying the mixture on to the filter material, and controlling the quantity of sprayed-on mixture to the amount of fiber material with reference to the infrared refiexion.

The requirements for the indicator substance to be used are as follows:

(a) the absorption band must be clearly distinguishable from that of cellulose acetate;

(b) the indicator must be miscible with the plasticizer on an ester base, at least in the quantity in which it is to be used with the plasticizer; and

(c) the indicator must not impair the curing or hardening of the plasticizer or its chemical absorption.

Preferably the indicator is an aliphatic polyglycol monoether.

A substance which has been found particularly suitable for carrying out the method of the invention is diethyleneglycol monoethylether. It is also possible to use diethyleneglycol monomethylether or triethylene'glycol monomethylether or triethyleneglycolmonoethyether alone or in mixture.

The invention will now be further explained with reference to the indicator diethyleneglycol monoethylether.

Diethyleneglycol monoethylether (referred to in what follows as DGME) can be determined quantitatively by measurement of infrared radiation at the wave length 7\=1.4,u and )t=3.5,a and can be mixed with esters suitable for use as plasticizers in the invention in any desired quantity.

Table 1 represents the results of tests and gives the ratio of the glycerine triacetate or diethyl citrate with 30% of DGME together with the voltage in mv. measured on an infrared measuring instrument produced by Mssrs. Peer, of Hattersheim, Germany. The measurements were carried out at t=1.4 and 7\=3.5;.t. The voltage measured can be used directly for controlling the quantity of plasticizer sprayed.

Since the results of measurement are immediately available and can be used for regulating the filter producing machine, the use of the method in accordance with the invention improves the economics of production because the addition of plasticizer can be held within extremely narrow tolerances. There is also the advantage that the machine is promptly corrected and waste is reduced.

A further advantage of the method in accordance with the invention is that, surprisingly, the indicator added, more particularly DGME, has the property of bringing about a substantial shortening in the time required for curing filter rod sections made of cellulose acetate and sprayed with an ester-type plasticizer. This shortening of the hardening time does not bring with it any reduction in the chemosorptive action as regards the removal of undesired tobacco smoke components.

The shortening of the hardening time not only cuts out the deformation of filter rod sections during stacking for hardening but also reduces difiusion of the plasticizer into the fibers since, obviously, once the plasticizer mass has hardened it cannot penetrate into the interior of the fibers. Since the plasticizer remains to a greater extent on the surface of the fibers its chemosorptive action is greater.

Table 2 gives analytical data for cigarette filters which were treated with equal quantities of glycerine triacetate and diethyl citrate with and without DGME. The data indicates the superiority of filters made with a plasticizer containing DGME as regards the removal of nicotine and phenol. The percentages are by weight and indicate the relative amount of plasticizer added to the filter material.

Despite the reduction in the total quantity of plasticizer to 30% of the original value there is no reduction in the degree of adsorption in the case of the use of DGME in accordance with the invention.

Table 3 gives the hardening times for various plasticizer compositions. The total quantities applied were so chosen that in all tests whose results are given in the table the final hardness corresponded with the minimum value found empirically to be satisfactory.

Hardness was measured with a device produced by Messrs. Filtrona, Glinde, Stormarn, Germany. The device measured ditferences in depths of penetration in units of 0.01 mm. with a loaded and an unloaded punch for a given period of time. In Table 3 a lesser depth of penetration denotes a greater degree of hardness of the filter rod sections.

TABLE 3.DEPTH OF PENETRATION IN 0.01 AIM.

N0. 2: Triacetln, N o. 4: CD, N0. 1: 30% plus 307 plus Triacetin, DGME, No. a; on, Donn, 100% by 70%, both 100% by 70%, both Weight by weight weight by weight N OTE.-C D =diethyl citrate.

The desired final hardness corresponded to a depth of penetration of 0.80 mm.

FIG. 1 of the accompanying drawings is a graph showing the progress of hardening of cigarette filter material with time. The vertical axis denotes the degree of hardness and the horizontal axis the time elapsing from the application of the plasticizer.

FIG. 2 is a graph representing the results set out in Table 3. The horizontal axis is calibrated in minutes (above) and hours (below). The lines of the graph correspond to the results obtained with materials given in columns No. 1, No. 2, No. 3, and No. 4 of Table 3. The horizontal line has been drawn at 0.80 mm. to indicate the desired depth of penetration.

What we claim is:

1. A process for the production of tobacco smoke filter material which comprises mixing an aliphatic polyglycol monoether indicator with a plasticizing agent for cellulose acetate fibers, the aliphatic polyglycol monoether being miscible with the plasticizer and having infrared absorption bands distinguishable from cellulose acetate, measuring the infrared reflection characteristics of the resulting mixture, applying the resulting mixture to spread out cellulose acetate fibers in tow form in an amount sufiicient to bind the fibers into a tobacco smoke filter material, the amount of the resulting mixture applied being determined by the infrared reflexion measurement.

2. A method in accordance with claim 1 in which the indicator is diethyleneglycol monoethylether.

3. A method in accordance with claim 1 in which the indicator is diethyleneglycol monomethylether.

4. A method in accordance with claim 1 in which the indicator is triethyleneglycol monomethylether.

5. A method in accordance with claim 1 in which the indicator is triethyleneglycol monoethylether.

6. A method in accordance with claim 1 in which the indicator is a mixture of at least two of the substances diethyleneglycol monoethylether, diethyleneglycol monomethylether, triethyleneglycol monoethylether, triethyleneglycol monomethylether.

7. A method in accordance with claim 1 in which the plasticizer comprises triacetin.

8. A method in accordance with claim 1 in which the plasticizer contains diethyl citrate.

9. In a process for producing cellulose acetate tobacco smoke filter material which comprises applying a plasticizer to spread out cellulose acetate fibers in tow form and curing the plasticizer cellulose acetate, the improvement which comprises mixing with the plasticizer prior to application to the fibers an aliphatic polyglycol monoether indicator miscible with the plasticizer and having infrared absorption bands distinguishable from cellulose acetate, measuring the infrared reflexion characteristics of the resulting mixture, spraying the mixture onto the filter 6 material and controlling the quantity of sprayed-on mix- References Cited ture by the measured reflexion.

10. The method of claim 9 in which the indicator is UNITED STATES PATENTS diethyleneglyocl monoethylethen 3,326,221 6/1967 Huffman et a1. 131267 3,370,595 2/1968 Davis et al. 13l267 X 11. The method of claim 9 in which the indicator is 5 a mixture of at least two of the substances diethylene- EDWARD wHlTBY, p i Examiner glycol monoethylether, diethyleneglycol monomethylether, triethyleneglycol monoethylether and triethyleneglycgl monomethylethen D 

